Subsurface iron removal for drinking water production: understanding the process and exploiting beneficial side effects ir. Doris van Halem1,2 ir. Weren de Vet1,3 prof. dr. Gary Amy1,2 prof. ir. Hans van Dijk1 1 Delft University of Technology, The Netherlands 2 UNESCO-IHE Institute for Water Education, The Netherlands 3 Oasen Drinking Water Company, The Netherlands CONTACT: D.vanHalem@TUdelft.nl/drinkwater.tudelft.nl

Lay-out of this presentation Introduction to subsurface iron removal Oasen drinking water company Subsurface arsenic removal Enhanced nitrification in biofilters November 18, 2008

Subsurface or in-situ iron removal periodical alternating Numerous applications in Europe: Van Beek, 1983; Rott and Friedle, 1985; Braester and Martinell, 1988; Rott and Lamberth, 1993; Mettler et al., 2001; Appelo et al. 1999; etc. November 18, 2008

Subsurface or in-situ iron removal (cont’d) Subsurface treatment in short injection of aerated water into anaerobic aquifer; (adsorbed) iron(II) is oxidized to iron(III); retardation of the oxygen front. November 18, 2008

Subsurface or in-situ iron removal (cont’d) Subsurface treatment in short iron (oxy)hydroxides promote iron(II) adsorption; abstraction of groundwater with decreased iron levels; also: adsorption of anions such as arsenic and phosphate Emphasize co precipitation and adsorption of P and As, not iron removal November 18, 2008

Oasen Drinking Water Company, the Netherlands 750.000 customers 10 production stations Water use p.p. 45 m3/y = 34 gallons p.d. Total Oasen annual: 47 million m3 = 12 billion gallons The Netherlands small, densly populated country, 8 times more population on 8 times smaller land area. Oasen rural area near Rotterdam Water consumption in NL relative low Annual production 12 billion gallons Closer look Oasen area: polders November 18, 2008

Oasen Drinking Water Company, the Netherlands (cont’d) The Netherlands: below see level Oasen: fenland and reclamed marches Oasen The Netherlands half under sea level (blue) =>“The low lands” Oasen in this area November 18, 2008

Oasen Drinking Water Company, the Netherlands (cont’d) Drinking water treatment plant operates “subsurface aeration” at multiple sites; for enhancement of nitrification, so not for iron or arsenic removal; a single well for injection and abstraction. in short: - arsenic concentrations very low (<10 ug/L) - 1% volume injection of volume abstraction - duration of cycle: approximately 1 month November 18, 2008

Oasen Drinking Water Company, the Netherlands (cont’d) Subsurface aeration: less intensive form of subsurface iron removal (i.e. less water is injected into the aquifer) Abstracted water is mixed with other groundwater sources before treatment. Injection water volume is only 6% of the abstracted volume from well 8 and 1% of the total abstracted volume of the whole well-field; Yet this limited amount has a high effect on nitrification in the production biofilters November 18, 2008

Oasen Drinking Water Company, the Netherlands (cont’d) Table 1Water quality parameters in reference wells around subsurface treatment well (LS-P08) Reference wells LS-P02 LS-P07 LS-P11 Ammoniuma mg L-1 NH4+-N 1.1 1.3 2.2 Arsenicb µg L-1 As (total) 5.1 2.9 Ironc mg L-1 Fe2+ 5.6 3.2 5.5 Manganesec mg L-1 Mn2+ 1.0 0.8 Phosphateb mg L-1 PO43- 0.9 Bicarbonateb mg L-1 HCO3- 265 222 282 TOCc mg L-1 C 2.3 2.8 Temperature °C 12 pH at 20°Cb - 7.2 7.4 a average 1992-2006 b average 1994-2005 c average 2003-2005 November 18, 2008

Oasen Drinking Water Company, the Netherlands (cont’d) Start subsurface iron removal November 18, 2008

Side effects Adsorption and co-precipitation of arsenic during subsurface iron removal -> subsurface arsenic removal Enhanced nitrification in dry biofilters after subsurface treatment Bron: Wikipedia Arsenicosis: chronic arsenic poisoning from drinking water Effects include changes in skin color, formation of hard patches on the skin, skin cancer, lung cancer, cancer of the kidney and bladder, and can lead to gangrene. The World Health Organization recommends a limit of 0.01 mg/L (10ppb) of arsenic in drinking water. This recommendation was established based on the limit of detection of available testing equipment at the time of publication of the WHO water quality guidelines. More recent findings show that consumption of water with levels as low as 0.00017mg/L (0.17ppb) over long periods of time can lead to arsenicosis. November 18, 2008

Arsenic occurrence and geochemistry Arsenate (V) typically in aerobic water (surface water) negatively charged Arsenite (III) typically in anoxic water (groundwater) uncharged more mobile and toxic than As(V) November 18, 2008

Arsenic occurrence and geochemistry (cont’d) Note: countries with very local arsenic problems due to mining or geothermal influences are not listed in this map Arsenic: a worldwide problem! November 18, 2008

Subsurface arsenic removal Oxidation-adsorption mechanism Arsenic adsorption onto iron hydroxides pH dependency competing anions (e.g. PO43-) high Fe:As ratio required Source: Sharma (2001) Source: Dixit and Hering (2003) November 18, 2008

Subsurface arsenic removal (cont’d) Source: Oasen Drinking Water Company November 18, 2008

Subsurface arsenic removal (cont’d) Does remobilization occur? Source: Oasen Drinking Water Company November 18, 2008

Ongoing arsenic research Simulation in the laboratory: regeneration of the iron surface (ii) Arsenic remobilization from accumulated iron precipitates (iii) Field study in rural Bangladesh November 18, 2008

Enhanced nitrification in biofilters Dry biofilters: coarse river sand (fraction 1.7-2.5 mm) Methane is effectively stripped before or during dry biofiltration by forced aeration. November 18, 2008

Enhanced nitrification in biofilters (cont’d) Subsurface aeration No subsurface aeration Subsurface aeration Effectiveness of SA on nitrification shown in graph Different treatment plant, same patron, vertical axis NH4 in effluent; in = 2,1 for this filter First period little removal After start of SA almost complete Relapse when SA stopped Total nitrification when restarted November 18, 2008

RT-PCR or Quantitative-PCR Real Time Polymerase Chain Reaction ©2005 by Steven M. Carr (http://www.mun.ca/biology/scarr/Principle_of_RT-PCR.html) Ammonia-oxidizing microorganisms Iron-oxidizing bacteria http://www.mycometrics.com/images/image_pcr1.jpg Erfelijk materiaal bestaat uit dubbelstrengs DNA moleculen, opgebouwd uit de nucleotiden A (adenosine), C (cytosine), T (thymine) en G (guanine). G bindt met C, A met T. De volgorde A,C, T en G is uniek voor ieder organsime! Vermenigvuldiging van een kenmerkend deel van het DNA met met PCR (‘Polymerase Chain Reaction’) November 18, 2008

Microbial growth in subsurface aerated well For more results on enhanced nitrification in biofilters is referred to the 4:30 presentation November 18, 2008

Thank you for your attention! ir. Doris van Halem1,2 ir. Weren de Vet1,3 prof. dr. Gary Amy1,2 prof. ir. Hans van Dijk1 1 Delft University of Technology, The Netherlands 2 UNESCO-IHE Institute for Water Education, The Netherlands 3 Oasen Drinking Water Company, The Netherlands CONTACT: D.vanHalem@TUdelft.nl/drinkwater.tudelft.nl